Continuous films of natural or synthetic resins are widely used in various fields including photography, printing, textile, paint industries or the like. Heretofore, such resinous films have been made as uniform, continuous films, whose properties and functions are regulated by the film constituting resin itself. Therefore, a number of synthetic high molecular compounds have been developed in answer to disverse needs. However, there is a limit to finding novel high molecular compounds due to the restrictions in natural resources, development costs, environmental pollution and the like.
On the other hand, from the viewpoint of diversification and advancement in requirements, various properties and functions are concurrently required in a single film material. This is almost impossible for the existing resinous materials.
Under the circumstances, attempts have been naturally made to use combinations of different resinous materials. For example, in the coating composition area, there have been developed solution type, emulsion type or powder type compositions containing as resinous vehicle two and more different type of resins and also a technique of using a combination of soluble resin and insoluble resinous particles. When applied, these compositions will give either one of the following coating structures. That is, one is a thoroughly melted uniform film and the other is heterogeneous film comprising a continuous phase of melted resins and a discontinous phase of insoluble resinous particles uniformly and finely dispersed in said continous phase. The matter need occasion no surprise because what was borne in mind was how to obtain a uniform film by all means.
According to the heretofore proposed techniques, it was, however, not possible to attain a film with improved properties of both constituent resins. That is, in the case of either uniformly melted films or heterogenous structure films, it was, not possible, as is well known in the art, to get the composite excellent properties of the respective resins. In such case, the final product shows cumulative inferior properties of these resins. For example, for the purpose of obtaining a product having improved tensile strength and elongation properties, even when a resin which has good tensile strength but poor elongation is used with B resin which is soft but has good elongation, it is not possible to obtain a product having expected properties and the resultant product is soft and of inferior elongation characteristics.
Therefore, the appearance of improved resinous films with each conflicting but desirable property such as tensile strength and elongation, water resistance and anticorrosive property, appearance and good film performance, and the like, which had never been attained with heretofore proposed uniform films and heterogeneous films has long been desired. Now, the inventors have found that when a second resin exists in the form of certain size of mass as discontinous phase, in a continous phase of first resin, desired properties of the said two resins will come out in thus obtained composite film, that the said mass may take either form of fused aggregate, unfused aggregate or crosslinked mass of fine particles, and that such composite film may be easily produced by using a resinous composition containing in a liquid medium, soluble resin, insoluble resinous particles and certain organic compound capable of promoting the formation of such aggregated mass of the insoluble resinous particles, hereinafter called as microdomain. On the basis of these findings, the present invention has been made.